They should change the mechanics of the Legendary Car Dealership where it's just like Brand Central where all available cars are there, but with elements of the Used Car Dealership (when you browse, some cars might be out of stock, and will have to be reserved, in the color/livery of your choice until it's available again). Kind of like how the classic dealerships in the first Test Drive Unlimited worked.
The only reason they have put LCD with a slow rotation:
They want more sales from MTX.
Its a tactic stolen from other successful F2P games. Having expensive, high sort after cars available for a limited time and no guarantee to when they will be back, creates a demand and a want for players to have it now. If they cant afford it now, they are forced to wait an undetermined amount of time for it to return or to purchase credits with real money. It also means that when it does return, they're going to spend their credits immediately on this car and have less credits available to them for other cars that they will also want.
In previous GT's, you could always sell old cars that you didn't use, or duplicate cars that you won multiple of for a quick instant cash boost but PD decided to keep this out of the game for the first time in any GT game...
The same goes with the car invites. They are all for expensive, highly sort after cars that are only available for a short amount of time.
The only reason that PD made updates to the economy, that helped the userbase actually get somewhere in this game was due to a mass bombing of the games metacritic scores after a even more blatant attempt slow down players credit earning potential was released in the form of an "update"
I believe that PD will continue there current practices, designing the game in a way to push its userbase towards purchasing credits, unless a massive outrage is heard again. This was in no way a planed moved by PD and was only done because the players forced their hand. Sadly - a majority of people still playing this game just accept this as the status quo of gaming and seem to be jumping to PD's defence and somehow even praising them for making some of the economy changes that they have...
(Making 1 off payments that only account for 10% of the total cost of cars is barely fixing anything imo)
We were incredibly lucky that the amount of cars available was doubled. Unless the players get loud and angry again, any further changes of this horribly slow and annoying system are incredibly unlikely.